The present invention relates to an image pickup device for television cameras which performs a shutter function.
Conventional image pickup devices of the type having a shutter function include, for example, one disclosed in Japanese Patent Application of JP-A-No. 56-44271 and another announced by Takeuchi, etc., at the national convention, 1982, of the Institute of Television Engineers of Japan under the title of "Driving Method for Vertical Overflow-Structure CCD Image Sensor". These devices are designed so that the shutter function is realized by reading the charges stored in the photodiodes prior to the reading of the effective signal by the overflow drains of the CCDs. With the CCD sensor, the vertical CCDs perform a memory function so that if the charges stored in the photodiodes are transferred to the vertical CCDs at the expiration of a given time (determined in accordance with the shutter speed) after the resetting of the photodiodes, the charges produced in the photodiodes during the given time are stored in the vertical CCDs. Then, by successively reading the charges from the vertical CCDs in synchronism with the transmission timing of a television signal, the video signal of a scene exposed for the given time is obtained.
The vertical CCDs function as a memory for one picture or frame. Therefore, any given shutter speed can be realized by selecting a time interval from the resetting of the photodiodes up to the transfer of the charges to the vertical CCDs.
In the case of a MOS sensor, however, a photodiode array is scanned by vertical and horizontal scanning circuits and the charges stored in the photodiodes are successively read. The MOS sensor includes no memory (vertical CCDs) for temporarily storing the charges of all the photodiodes as in the case of the CCD sensor and therefore the shutter function cannot be realized by the method stated in the previously mentioned literature.
On the other hand, if an image sensor adapted for a two-line-at-a-time reading is to be provided with a shutter function, there is a disadvantage that the lines are not the same in signal quantity and therefore flicker is caused in a picture reproduced on the face plate of a television receiver.